[M4tt0]

Chaps, the 25Hz refreshrate referred to the old settings FernetMenta asked for! When chosing 1920x1080 resolution, that was set automatically. My - possibly naive - assumption was that 1920x1080 at 25Hz (for the full picture) corresponds to 1920x540 at 50Hz (for two half-pictures) (=1080i) so I did not question it at the time.

With 720p I can run 60 or 50Hz and am running 50Hz currently (just as fritsch suggested two days ago).